This section temporarily contains information copied directly from Bulbapedia, and needs to be rewritten so not to be classified as plagiarism.
Tyrantrum is a large, dinosaurian Pokémon, closely resembling theropods like Tyrannosaurus. It is predominantly brick-red in coloration, with scaly patterns on its skin and scattered orange highlights on some of the scales and ridges. The underbelly is gray with white borders, and it has a long tail with two orange spikes near the tip. Its small forelimbs have only two black clawed digits, but it has powerful hind legs with three sharp, black talons. Plated, armor-like ridges are found on the front of the legs and down the back and tail. Spiky, white "fluff", similar to the primitive feathers on many dinosaurs, extends into a cape-like fringe around the neck.
Additional feathering forms a prominent beard on the lower jaw, which is otherwise gray in coloration. Its head is proportionally large, with a ridged snout and powerful jaws. The lower jaw is lined with pointed teeth, and the upper jaw features a number of tooth-like projections which are also highlighted orange. Its eyes appear to have black sclera with white irises. An orange, five-pointed crest extends from the snout above the eyes and point backwards, giving it the appearance of wearing a crown.
Before its extinction, wild Tyrantrum used to live 100 million years ago, when its powerful jaw conferred its status as an unmatched predator. Since it was considered invincible in the ancient world, it behaved like a king.